Many people give children away but usually only in the communities where that is encouraged. There are families who are ashamed of their children. And there are many people who look down and children (and families) with special needs, so you can not blame the families!
Excuse me, but that is an absolutely untrue and offensive comment! Who said siblings will get “2nd tier” shidduchim?? There are MANY people who have siblings and are very happpily married even without the “huge positive”. I’d love to know where you got your info from!